NEARLY EVERYBODY takes caffeine in some form or the other: tea, coffee, cola, chocolate, cocoa, over-the-counter cold remedies and sports drinks. Caffeine improves mood and alertness temporarily, but it also influences exercise performance and affects exercise physiology enough to make it a restricted substance under the IOC's anti-doping laws. Caffeine is also a significant presence in playgrounds all over the world thanks to prominent sports personalities who plug cola drinks in ads that portray them as refreshing, thirst-quenching energy drinks, and a rising proportion of sports drinks popular among gym goers contains mega doses of caffeine.

Caffeine consumption is nearly universal and all of us must exercise for a healthy life, so it is important to understand caffeine's effects on the body and its upper limit of safety.

Caffeine levels peak in the blood within two hours of consumption, and it takes around six cups of coffee taken one hour before exercise for levels to reach those prohibited by the IOC, but even two cups of coffee taken an hour prior to exercise increases endurance. Caffeine delays fatigue and improves the subjective sensation of effort, but its effects on muscle metabolism are less clear. In high doses, muscles break down fat and spare carbohydrate: this plays a role in delaying fatigue, but this effect apparently does not occur with the average cup of tea. Caffeine improves endurance in exercise that lasts for 5 minutes or more, but it does not improve sprinting performance or anaerobic exercise (e.g., intense weight training) that lasts less than 90 seconds, which means that caffeine-laden sports drinks are just an expensive and useless indulgence for athletes and bodybuilders.

Caffeine is also a diuretic, and a large dose (a few cups of coffee) robs the body of precious water essential for exercising muscles. Poor hydration can cause cramps and increase the risk of injury, but these effects are not significant with the average cup of tea in a fully hydrated person.

In higher doses, caffeine's side effects include anxiety, irritability, diarrhoea, insomnia, arrhythmias, hallucinations and impaired intellectual performance. These side effects worsen with age. Old people are likely to suffer from insomnia and disorders of heart rhythm with even a regular cup of tea.

Caffeine is a stimulant drug that is harmful in high doses, and it makes sense to avoid it before exercise despite research that suggests a cup of tea may do little harm. Such research happens mostly on fit athletes and it is difficult to extrapolate the results to non-athletes with relatively unfit bodies. If you must have a cup of tea before your workout, make sure you drink a couple of glasses of water before you take the first sip.